Transfer of generic Escherichia coli and attenuated Salmonella enterica Typhimurium from the soil to the surface of in-shell pecans during harvest

Authors: Bardsley, Cameron; Chasteen, Kaicie; Shapiro Ilan, David; Bock, Clive; Niemira, Brendan; DEV KUMAR, GOVINDARAJ - University Of Georgia

Submitted to: Heliyon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2023
Publication Date: 8/30/2023
Citation: Bardsley, C.A., Chasteen, K.S., Shapiro Ilan, D.I., Bock, C.H., Niemira, B.A., Dev Kumar, G. 2023. Transfer of generic Escherichia coli and attenuated Salmonella enterica Typhimurium from the soil to the surface of in-shell pecans during harvest. Heliyon. https://doi.org/10.1016/j.heliyon.2023.e19676.
DOI: https://doi.org/10.1016/j.heliyon.2023.e19676

Interpretive Summary: Foodborne pathogens such as Salmonella or E. coli O157:H7 can be present in the soil in pecan orchards. While pecans are being harvested they fall to the ground and can become contaminated with foodborne pathogens. If this were to happen it would have the potential to make consumers sick if the product wasn't properly treated or handled. It is really important to understand if pecans can be contaminated with these pathogens during harvest in order to determine ways to eliminate pathogens once they are on the pecan shell or implement strategies to reduce the chance of pecans being contaminated during harvest. The results of this study show that pecans are capable of being contaminated during harvest and that weather factors and the pathogen levels in the soil play a role in pecan contamination.

Technical Abstract: During harvest pecan nuts are at risk of contamination with foodborne pathogens from extended contact with the ground. The objective of this study was to determine the potential transfer of Escherichia coli and Salmonella from the ground to in-shell pecans during the harvesting process. Plots were sprayed with 1 liter of a rifampicin resistant strain of either E. coli TVS 353 or an attenuated Salmonella Typhimurium inoculum at a low (~4 log CFU/ml), mid (~6 log CFU/ml) or high (~8 log CFU/ml) concentrations. The following day, nut samples from each plot were collected at 1 min, 4 h, and 24 h following harvest. Samples were enumerated. The Salmonella inoculated plots were 2.0±0.3, 4.1±0.1, and 6.4± 0.2 log CFU/g for the low, mid, and high inocula, respectively. The E. coli inoculated plots were 1.5±0.4, 3.7±0.3, and 5.8±0.1 log CFU/g for the low, mid, and high inocula, respectively. There was a significant difference in the average daily rainfall among the three trials. Trial 3 received 23.8±9.2 cm, while trials 1 and 2 received much less (0.1±0.1 0.0±0.0 cm, respectively). Inoculation concentration and trial were significant (P<0.05) factors that influenced the transfer of E. coli and Salmonella to pecans. For the high inoculum treatment, bacterial transfer to pecans ranged from 0.7±0.3 to 4.1±0.2 for E. coli and 1.3±0.7 to 4.3±0.4 log CFU/g for Salmonella. For the medium inoculum treatment, transfer ranged from <0.3 to 1.5±0.1 for E. coli and <0.3 to 1.9±0.2 log CFU/g for Salmonella. For the low treatment, transfer ranged from <0.3 to 0.4±0.2 and <0.3 to 0.5±0.1 log CFU/g for E. coli and Salmonella, respectively. Trial 3 had significantly less transfer overall for all inoculum levels, most likely due to the greater rainfall compared to the other trials. These results show the need for implementing agricultural practices that prevent potential transfer of foodborne pathogens onto the surface of in-shell pecans during harvest.